Buggy code:
public class ModelControllerMBeanHelper { static final String CLASS_NAME = ModelController . class . getName ( ) ; private final boolean standalone ; private final ModelController controller ; private final PathAddress CORE_SERVICE_PLATFORM_MBEAN = PathAddress . pathAddress ( PathElement . pathElement ( "core-service" , "platform-mbean" ) ) ; private final TypeConverters converters ; private final ConfiguredDomains configuredDomains ; private final String domain ; ModelControllerMBeanHelper ( TypeConverters converters , ConfiguredDomains configuredDomains , String domain , ModelController controller ) { } int getMBeanCount ( ) { } Set < ObjectInstance > queryMBeans ( final ObjectName name , final QueryExp query ) { } Set < ObjectName > queryNames ( final ObjectName name , final QueryExp query ) { } PathAddress resolvePathAddress ( final ObjectName name ) { } MBeanInfo getMBeanInfo ( final ObjectName name ) throws InstanceNotFoundException { } Object getAttribute ( final ObjectName name , final String attribute ) throws AttributeNotFoundException , InstanceNotFoundException , ReflectionException { } AttributeList getAttributes ( ObjectName name , String [ ] attributes ) throws InstanceNotFoundException , ReflectionException { } private Object getAttribute ( final ResourceAndRegistration reg , final PathAddress address , final ObjectName name , final String attribute ) throws AttributeNotFoundException , InstanceNotFoundException , ReflectionException { } void setAttribute ( ObjectName name , Attribute attribute ) throws AttributeNotFoundException , InstanceNotFoundException , InvalidAttributeValueException { } AttributeList setAttributes ( ObjectName name , AttributeList attributes ) throws InstanceNotFoundException , ReflectionException { } private void setAttribute ( final ResourceAndRegistration reg , final PathAddress address , final ObjectName name , final Attribute attribute ) throws AttributeNotFoundException , InstanceNotFoundException , InvalidAttributeValueException { } ObjectInstance getObjectInstance ( ObjectName name ) throws InstanceNotFoundException { } Object invoke ( ObjectName name , String operationName , Object [ ] params , String [ ] signature ) throws InstanceNotFoundException , MBeanException , ReflectionException { } private Object invoke ( final OperationEntry entry , final String operationName , PathAddress address , Object [ ] params ) throws InstanceNotFoundException , MBeanException , ReflectionException { } static InstanceNotFoundException createInstanceNotFoundException ( ObjectName name ) { } private ResourceAndRegistration getRootResourceAndRegistration ( ) { } private ModelNode execute ( ModelNode op ) { } private ImmutableManagementResourceRegistration getMBeanRegistration ( PathAddress address , ResourceAndRegistration reg ) throws InstanceNotFoundException { } private String getFailureDescription ( ModelNode result ) { if ( result . hasDefined ( FAILURE_DESCRIPTION ) ) { <START_BUG> return result . get ( FAILURE_DESCRIPTION ) . asString ( ) ; <END_BUG> } return null ; } private String findAttributeName ( ModelNode attributes , String attributeName ) throws AttributeNotFoundException { } private boolean isExcludeAddress ( PathAddress pathAddress ) { } public static ObjectName createRootObjectName ( String domain ) { } }

Fix:
return result . get ( FAILURE_DESCRIPTION ) . toString ( ) ;